The objective of this proposal is to develop criteria to aid in the appropriate selection of patients with chronic aortic and/or mitral regurgitation for valve replacement. Criteria will be based on non-invasive determinations of left and right ventricular myocardial function, made with radionuclide cineaniography at rest and during exercise, and echocardiography at rest, so that results will be easily applicable for repeated periodic assessments in patients not considered to be candidates for catheterization and operation on the basis of current clinical criteria. The study will focus on 1) determination of objective pre-operative predictors of post-operative clinical and myocardial functional results in patients who undergo valve replacement, and 2) determination of objective predictors of future development of symptoms and of irreversible myocardial dysfunction in patients not yet considered to be operative candidates by currently accepted criteria. In addition to assessment of systolic contractile function, the study will utilize invasive and non-invasive methods to determine the prognostic importance of left ventricular diastolic properties assessed prior to operation.